1. Field of the Invention
The invention is directed to a needle comprising a hollow rigid needle tube having one side wall at the front end of the needle tube which is curved toward the opposite, axial side wall. A lumen opening is formed in the axial side wall in a region near the curved side wall. The lumen opening extends substantially parallel to the longitudinal axis of the needle tube and is provided with a front punctuating portion and a rear inner cutting edge arranged on the inner surface of the axial side wall.
2. Description of Related Art
A known needle is disclosed in U.S. Pat. No. 2,746,454. Insertion of such a needle into a blood vessel without danger of hurting the opposite wall of the vessel is facilitated by the front punctuating portion of the needle being formed as a hook. The strongly curved back surface, opposite the comparatively short lumen opening, acts as a gliding surface. The foremost round edge of the punctuating portion is directed transversely to the longitudinal axis of the needle tube (towards the side) and is in alignment with the outer surface of the needle tube. The round edge is free of a plane bevel, whereas the rear edge of the lumen opening is beveled to thereby form an inner cutting edge.
For making good use of its curved sliding surface, a needle of this kind is inserted into a blood vessel along a curved path. The course of the curved path substantially corresponds to the radius of curvature of the sliding surface of the punctuating member. Due to this angular positioning of the needle during punctuation (which is unavoidable because of the hooked curvature), the sharp rear cutting edge of the lumen opening punches out material from the surface opening. The punctuating opening is thereby enlarged. This produces a disadvantageous traumatic effect when punctuating tissue.
This punching out effect (or punching effect) is also not desirable when the needle is used to refill a device for administering medication. Such a device for administering medication might comprise, for example, an implanted capsule having a cavity for receiving the medication and being connected to a catheter. The free end of the catheter would lead to an infusion site and would supply medication thereto. The outwardly directed wall (directed towards the skin of the patient) of the implanted capsule would consist of a perforable elastomeric diaphragm which is punctuated by the needle for refilling medication into the cavity of the capsule.
According to the prior art, repeated punctuating of a needle into the diaphragm of the capsule causes leakage of the diaphragm because the edge of the bevel eye punches out elastomeric material. This creates holes that do not close again by themselves. After a comparatively small number of punctures, the capsule starts leaking, thus forcing the user to exchange at least the capsule of the administering device. Besides, punched-out particles of the material that are carried along into the medication system cause contamination of the medication.
Up to now, so-called Huber needles have been used as refill needles. In one presently used embodiment of such Huber needles, the whole needle tube has its front end kinked obliquely sidewards. The front end of the needle tube section is provided with a lumen opening which extends substantially in parallel to the longitudinal axis of the needle tube and which is beveled circumferentially.
In such needles, the lumen opening is arranged far outside of the contour of the straight needle tube section. Even upon correct vertical positioning of the Huber needle, this fact causes material particles to be punched out. This is because the angled front portion of the needle tube, like a wedge, penetrates the surface from one side. The rear cutting edge of the bevel (which cutting edge is opposed to the wedge) is pressed laterally against the material to be penetrated and thus shears off material that has entered into the opening. When the needle tip is incorrectly pierced obliquely into the surface to be punctuated, even more wall material penetrates into the lumen opening. As a consequence, still larger material portions are sheared off by the exposed cutting edge of the rear bevel eye of the lumen opening.
In another embodiment of the Huber needle comprising a laterally directed lumen opening (U.S. Pat. No. 2,409,979), one side wall of the needle tube is diverted toward the opposite axial side wall obliquely and without curvature. The edging surrounding the lumen opening is ground flatly and tangentially to the outer surface of the needle tube and has its rear edge area provided with a cutting edge sloping from the outside to the inside, i.e. an outer cutting edge. The punctuating portion, the tip of which is in alignment with the outer circumference of the axial side wall, is provided with a facet grinding on the edging of the lumen opening.
Practice has shown that during punctuation of an artificial or natural surface, the oblique surface of the needle tube causes a one-sided wedge effect which impedes the formation of a non-widened, sharp cut. Upon advancing of the needle, material is pressed into the lumen opening. The material is cut off at the rear cutting edge and is damaged by squeezing.
The problem of considerable wall punchings by the rear cutting edge of a bevel eye also occurs when using another known needle (disclosed in DE-OS-No. 30 13 384) which is provided with a ground oblique lumen opening in its front region. A tip extends at an angle from the front end of the lumen opening. The outer end of the angled tip is arranged substantially on the central axis of the needle tube. The rear cutting edge of the bevel eye is arranged at the rear end of the lumen opening without the contour of the needle tube. When piercing a surface to be punctuated, a considerable punching effect is caused by an S-shaped curved path along which the tip is guided because of the mutual orientation of the parts of the front end of the needle tube. This punching effect is equally undesired when punctuating artificial and natural walls (diaphragm and body tissue).
It is an object of the present invention to improve the initially mentioned needle in such a manner that punching effects are eliminated during punctuation of a natural or artificial wall so that during use of the needle (e.g. as a spinal needle) damage to tissue is prevented, and during use of the needle as a refill needle the leak-proof condition of the implanted capsule of a device for administering medication is guaranteed even after several hundred punctuations.